The invention disclosed in this application relates to fuel injectors for internal combustion engines, specifically for Cummins diesel engines of the general type used in large trucks and construction equipment.
For many years, injectors of the general type known as "pressure-time-delivery" (PTD) injectors have been used in diesel engines of the type described above. These PTD-type injectors are simple and reliable, but do not provide precise control of the fuel injection process. This is because the plunger is limited in its downward movement when fuel is actually being injected into the cylinder, but not in its upward movement. The plunger and the return spring communicate through the upper end of the injector body into contact with the cam drive either directly or through a suitable linkage. Therefore, the PTD-type injector plunger is permitted free movement in its return stroke, subject only to limitations imposed by the cam linkage.
It has been observed for many years that the lack of precise adjustment in the upward direction of movement of the plunger results in fuel dribbling through the fuel sac holes between injections. This causes wasted fuel and smoking. In addition, overrun of the plunger to its top position, if not precisely adjusted, can cause exhaust gases to be forced into the injector through the sac holes. These extremely hot gases are then carbonized on the interior walls of the injector, causing fouling of the injector and premature wear and replacement.
Because of these problems, a new type of injector, called a "Top Stop-Type" injector has been developed. This type of injector gives much better emission control because the plunger is pre-set and does not require further adjustment in the engine. Fuel can be controlled more directly and more precisely and fuel dribbling between injections is therefore minimized or eliminated. As a result of the development of the top stop-type injector, the old, open top PTD-type injectors are no longer being installed in most new Cummins engines. Furthermore, as existing engines are overhauled, PTD injectors are being replaced with new, top stop injectors.
However, new top stop injectors are very expensive and add substantially to the overhaul costs of an engine when they are substituted for the old PTD-type injector.
In addition, replacement of PTD-type injectors with top stop injectors has created a vast supply of old PTD injector cores which are no longer suitable for use and therefore have little or no market value. Therefore, the invention disclosed in this application is directed to a means by which obsolete PTD-type injectors can be remanufactured into top stop injectors for a fraction of the cost of new top stop injectors, simultaneously reducing the cost of converting to the more efficient injectors while making use of a large supply of otherwise useless PTD injectors.